European regulators on Wednesday slapped Google with a roughly $1.7 billion fine on charges that its advertising practices violated local antitrust laws, marking the third time in as many years that the region's watchdogs have penalized the U.S. tech giant for harming competition and consumers.

Margrethe Vestager, the European Union's top competition commissioner, announced the punishment at a news conference, accusing Google of engaging in "illegal practices" in a bid to "cement its dominant market position" in the search and advertising markets.

The new penalty adds to Google's costly headaches in Europe, where Vestager now has fined the tech giant more than $9 billion in total for a series of antitrust violations. Her actions stand in stark contrast to the United States, where regulators - facing a flood of complaints that big tech companies have become too big and powerful - have not brought a single antitrust case against Google or any of its peers in recent years, reflecting a widening transatlantic schism over Silicon Valley and its business practices.

Google did not immediately respond to a request for comment.

In 2018, Vestager took aim at the company's Android smartphone operating system, claiming that Google pressured mobile device-makers to pre-install the tech giant's apps. A year before that, Vestager punished Google for giving its shopping-comparison service a better placement in search results over rivals' offerings. In both cases, Google has started tweaking its business practices in Europe to comply with the law while appealing the EU's decisions in court.

The company's changes include a new effort, detailed Tuesday, to help owners of Android smartphones find and use competing search and web-browsing services. But the update only applies to Europe, Google said in a blog post, without elaborating if it would alter some of mobile practices in the United States.

Vestager's latest punishment targets Google's relationships with third-party websites, from large retailers to small gossip blogs. Sites that participated in Google's "AdSense for Search" program could take advantage of Google's search tools on their web pages, and users who searched those sites would see results alongside ads served up by Google.

But Google prohibited those third-party sites from using rival ad services, one of many restrictions on AdSense customers that led the European Commission to conclude in an initial complaint filed in 2016 that Google had acted anti-competitively. EU officials did acknowledge at the time that Google had changed its AdSense contracts to allow for "more freedom to display competing search ads."

The EU's fine against Google is only its latest broadside against the tech industry. Vestager previously has acknowledged an ongoing antitrust investigation against Amazon, and earlier this month, she said the probe is in a "quite advanced" stage.

Music-streaming site Spotify, meanwhile, has urged European regulators to take similar aim at Apple, alleging last week that the iPhone giant has an "unfair advantage" because of the subscription-related fees it charges certain app makers. And individual European countries - emboldened with tough online privacy laws that took effect last year - also have set their sights on Silicon Valley. A key regulatory agency in Ireland recently confirmed that it has opened 10 probes into Facebook and its data-collection practices.

Google still could face additional penalties in the EU, where Vestager - who has emerged as one of Silicon Valley's toughest regulators - is set to finish her term as competition commissioner at the end of October. Regulators recently have started scrutinizing Google's handling of local search results, following a complaint brought by Yelp last year.